Originating in the Low Countries, Brethren schools provided poor students with food, books, paper, and lodging rather than forcing them to beg. The Brethren taught a new form of piety known as the Devotio Moderna, the modern devotion. True spirituality is within us, not in religious customs, for did not Jesus say, The kingdom of heaven is within you? In the inmost depths of our hearts, we may hear the voice of God.
What good does it do, Groote asked, for a man merely to go to church? He must do more than listen to his preacher. A man must train his conscience by studying for himself.
Groote also said that devout women who serve God in the privacy of their homes, without taking monastic vows, are just as religious as nuns in their convents. To love God and worship him is religion; not the taking of special vows. If one’s goal is to live a religious life, then his life becomes religious in God’s opinion and according to the judgment of conscience. It all comes down to two things: Love God and love man.
Source: The Brethren of the Common Life